The use of optical fibers for communications is growing at an unprecedented rate. A typical optical fiber comprises a glass fiber which is drawn from a preform and which has an uncoated diameter of about 125 microns and a coated diameter of about 250 microns.
Subsequently, the drawn optical fiber may be marked for purposes of identification in the field. Identification becomes necessary inasmuch as some cables which are shipped to the field are not preconnectorized in the factory. Also, if cables in the field are damaged such as by inadvertent impact with construction equipment, it becomes necessary to splice optical fibers to replace the damaged portions. Further, as fiber distribution networks expand, midspan entries often are used in order to tap signals at various critical locations, thus emphasizing the need for unit and fiber identification.
Generally, an optical fiber is identified by a marking which is provided on the outer surface of the coated fiber. Typically, the marking is continuous along the length of the fiber; however, additional identifiers are needed as the menu of standard colors is consumed. The marking may comprise inked indicia which are spaced along the length of the optical fiber. Such additional identifiers may include markings which are about 0.25 inch long and spaced apart about 0.25 inch. The ink which is used to mark the fibers typically is a permanent ink possessing viscosities compatible with the application technology at operating temperatures. In wheel type applicators, each inked indicium is applied about only two thirds of the periphery of each optical fiber. This is helpful to the retention of the indicia during particular tests of the marked fiber which are made when the fiber is wrapped about a mandrel, for example.
As can be imagined, the prior art includes arrangements for marking elongated strand material and for marking optical fibers. One such arrangement for elongated strand material is shown in U.S. Pat. No. 3,176,650 which issued to H. L. Woellner on Apr. 6, 1965. In that apparatus, a disc is mounted for rotation about an axis which is angled to the path of travel of an advancing elongated strand material. As the disc turns, a marking medium is flowed radially outwardly to ports to allow the marking medium to be slung into contact with the elongated strand material.
As for optical fibers, it has been customary to advance a fiber across and in engagement with a wick or wheel to which a marking ink is supplied. A cam is used to engage the moving optical fiber and intermittently to disengage the optical fiber from the wick to thereby provide spaced indicia along the fiber for dashing purposes. In addition, methods involving serrated wheel arrangements matched to line speed have been employed. Problems have occurred in the use of such an arrangement. The indicia, typically in the form of dashes, are not uniform and it is difficult to synchronize the movement of the cam with the line speed of the optical fiber.
In another commercially available apparatus, a grease-like ink is pumped upwardly into an application chamber through which an optical fiber is being advanced into engagement with an applicator wheel. It has been found that this arrangement requires a thorough cleaning after it had been used to mark about 1000 meters of fiber. Also, there is no provision for overflow of the ink. Consequently, it is difficult to control the quantity of ink in the application chamber. If there is too much ink, the applicator wheel becomes clogged; if there is too little, it is starved.
Another desired capability of an inking apparatus is that its geometry permits a plurality of such apparatus to be arranged side-by-side to ink a plurality of optical fibers moving in parallel paths prior to the assembly of the fibers into a ribbon or simply for purposes of efficient use of manufacturing space. Many commercially available marking arrangements are too bulky to permit such side-by-side use to mark a plurality of optical fibers which are moving along closely spaced paths.
A technique of marking a plurality of side-by-side elongated strand materials such as optical fibers includes the step of advancing each optical fiber along a path of travel which extends through a chamber. In the chamber is provided a supply member which in a preferred embodiment is porous and resilient and is capable of holding a liquid marking material which is adapted to mark an outer surface of the optical fiber. The liquid marking material is provided to the supply member in a controlled manner. An applicator member having a groove in a portion of its periphery is mounted for movement between the path of travel and engagement with the supply member and such that increments of length of each optical fiber are received in and then removed from the groove. The method also includes the step of moving the applicator member to engage compressively portions of the applicator member with the supply member and cause liquid marking material to be transferred from the supply member to the groove and from the groove to a predetermined peripheral portion of increments of length of each advancing optical fiber.
As the wheel is turned, the grooved portion is moved past and in engagement with a porous, resilient member which is saturated substantially with an ink. The mounting is such that the wheel compresses the porous member as it is moved therepast. This causes ink to fill the groove as the periphery of the wheel is advanced through its engagement with the porous member. Ink is supplied to the porous member through a tube, an end of which is disposed above the porous member. Excess ink falls to the bottom of the chamber where it is allowed to drain from the chamber and be returned to a supply. See U.S. Pat. No. 4,619,842 which issued on Oct. 28, 1986 in the names of P. A. Moss and F. A. Rotoloni.
The geometry of this last-described arrangement is such that a plurality of the applicator wheels can be placed side-by-side to mark simultaneously a plurality of advancing optical fibers which are spaced apart slightly. In one embodiment, the paths of the side-by-side fibers through apparatus are spaced apart about one-half of an inch.
One of the problems associated with the last-described apparatus is wear. It has been found that the portions of the apparatus which transfer the marking material to the optical fiber are subject to wear and or damage. Accordingly, the apparatus must be inspected periodically and replaced or maintained as is necessary.
Another problem relates to cleanliness of presently used marking apparatus. For example, the ink may be picked up by marking discs in an open container and transferred to the moving fiber. With the openess of the container and exposure of marking wheels to the ambient environment, the marking ink could become invaded by contaminants which could be transferred to the optical fiber. Additionally, in a system which involves an open chamber, ink viscosities may readily vary, and subsequently alter run conditions even during the length of a single optical fiber.
Clearly, what is needed and what does not seem to be available in the prior art are methods and apparatus for coating strand material in a way in which problems of wear and contamination are overcome. Such methods and apparatus must be relatively inexpensive to implement in order not to add unintentional cost to the product. More particularly, there is a need for methods and apparatus for marking optical fibers in a uniform manner to facilitate field identification. The sought-after apparatus should be one which can be placed side-by-side with other identical apparatus to mark a plurality of optical fibers being advanced side-by-side in closely spaced relation to one another.